Semiconductor lasers are commonly used in optical transceivers for telecommunications and data communication networks. The lasers used in such optical transceivers are commonly of the edge-emitting type. The edge-emitting laser of an optical transceiver is commonly coupled to the fiber with an aspheric lens or other discrete optical element because the light that the laser emits is not focalized or collimated, i.e., it diverges in a cone shape as it propagates. While the use of lenses to couple edge-emitting lasers to fibers in optical transceivers works reasonably well, it would be desirable to improve transceiver manufacturing economy by minimizing the number of transceiver parts and the attendant steps needed to achieve optical alignment among them.
Edge-emitting lasers for optical transceivers are fabricated on semiconductor wafers using standard photolithographic and epitaxial methods, diced into chips, and portions of each chip coated with reflective and anti-reflective coatings. The finished chips can then be tested. It would be desirable to minimize the number of manufacturing steps as well as to enhance testability.
Surface-emitting laser chip devices, in which a diffractive lens is integrated with an edge-emitting laser on the same chip, have been described. For example, in U.S. Pat. No. 6,459,716 to Lo et al. a device is described in which the edge-emitted beam is reflected by an angled surface toward a lower reflective surface that is parallel to the beam-emission direction and parallel to the chip surface, which in turn reflects the beam upwardly in a direction generally perpendicular to the chip surface, where it is emitted through a diffractive lens formed in a material on the chip surface. A transceiver having such a device can be manufactured more economically than one in which a separate lens is included. Nevertheless, the device is not straightforward to fabricate due to the inclusion of a waveguide to direct the beam from the laser toward the angled surface. Also, the geometry of the device may make its optical characteristics sensitive to wafer thickness errors.
It would be desirable to provide a device in which a laser and diffractive lens are monolithically integrated, and that is economical to manufacture. The present invention addresses these problems and deficiencies in the manner described below.